The present invention is related to a magnetic floating bearing of a fan, in which by means of distribution of magnetic force, the rotary shaft fitted in an inner magnetic ring is restricted within an outer magnetic ring to rotate in a floating state.
A ball bearing or oil-bearing bearing is applied to a fan for reducing resistance against the rotary shaft of the fan. However, when rotated, there is still frictional force exerted onto the shaft to produce noise. FIG. 1 shows a magnetic floating bearing of a heat-radiating fan. The bearing includes a base seat 80 having an upright sleeve. At least one magnetic hollow cylinder 81 is annularly disposed on inner wall of the sleeve. In addition, at least one magnetic ring 82 is fitted around lower section of the rotary shaft 83 corresponding to the magnetic hollow cylinder 81. The magnetic ring 82 is repelled downward by the magnetic hollow cylinder 81. Accordingly, when the rotary shaft 83 is fitted into the upright sleeve, the rotary shaft 83 is kept pulled downward. When rotated, the magnetic ring 82 fitted around the rotary shaft 83 is not in contact with the magnetic hollow cylinder 81. However, the magnetic ring 82 is repelled downward by the magnetic hollow cylinder 81 so that the rotary shaft 83 is pushed downward and the bottom end 831 of the rotary shaft abuts against upper face of a board 84. Accordingly, when the rotary shaft 83 rotates, the board 84 will still exert a frictional force against the bottom end 831 of the rotary shaft 83. This will reduce rotational efficiency. Moreover, after a period of use, the bottom end 831 of the rotary shaft 83 and the board 84 will be worn out and the using life of the fan will be shortened.
FIG. 2 shows another type of conventional magnetic floating bearing structure including a magnetic rotary shaft coupling section 91 fixedly fitted around the rotary shaft 92 and projecting therefrom. The upper and lower ends of the coupling section 91 are formed with slopes 911. The bearing structure further includes a recessed magnetic locator coupling section 93 fixedly annularly fitted in the locator. The upper and lower ends of the locator coupling section 93 are formed with slopes 931. The slopes 931 and the slopes 911 of the rotary shaft coupling section 91 magnetically repel each other, whereby the rotary shaft 92 is rotatably restricted within a certain range. However, the slopes 911 of the rotary shaft coupling section 91 and the slopes 931 of the locator coupling section 93 must have equal inclination angle so as to exert equal upward and downward axial forces F1, F2 onto the rotary shaft 92 and make the rotary shaft coupling section 91 float between the locator coupling sections 93. Accordingly, the rotary shaft 92 can rotate without suffering frictional force. However, the manufacturing and assembling procedure of the magnetic floating bearing necessitates high precision so that the manufacturing cost is relatively high. Moreover, the rotary shaft coupling section 91 radially floats between the locator coupling sections 93 simply by means of the transverse component force created between the inner and outer slopes 911, 931. The transverse centrifugal force created when the fan rotates is the main force applied to the bearing. The transverse component force is quite limited and there is no support around the rotary shaft coupling section 91. Therefore, simply relying on the little transverse component force created between the inner and outer slopes 911, 931, the rotary shaft can hardly bear the transverse force when rotating at high speed. As a result, the rotary shaft will inevitably transversely severely shake.
It is therefore a primary object of the present invention to provide a magnetic floating bearing of a fan, which locates rotary shaft by means of distribution of magnetic force. The magnetic floating bearing includes: an outer magnetic ring formed with a central axial through hole, an upper and a lower ends of the wall of the through hole having a magnetic strength greater than that of a center of the wall; and an inner magnetic ring formed with a central axial fitting hole in which a rotary shaft is snugly fitted, the polarity of an outer circumferential wall of the inner magnetic ring being identical to the polarity of the wall of the through hole of the outer magnetic ring, an upper and a lower ends of the outer circumferential wall of the inner magnetic ring having a magnetic strength less than that of a center of the outer circumferential wall. The upper and lower ends of the wall of the through hole of the outer magnetic ring respectively exert greater magnetic repelling force onto the center of the outer circumferential wall of the inner magnetic ring. Therefore, the inner magnetic ring is rotatably restricted and located within the outer magnetic ring without upward or downward detaching therefrom.
The present invention can be best understood through the following description and accompanying drawings wherein: